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Base station and cellular wireless communication system

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Title: Base station and cellular wireless communication system.
Abstract: A femtocell base station collects the terminal distribution within the cell and selects terminals to represent the cell-center and the cell-edge from among the terminals within the cell. The femtocell base station also calculates maximum transmit power for the respective the cell-center and cell-edge terminals allowable by the macrocell base station. The femtocell base station sets the respective transmit power of the cell-center and the cell-edge in a range that will not exceed the maximum transmit power, adjusts the transmit power control parameter to allow control by the terminal at the power value that was set, and notifies the terminal. Communication with high throughput can in this way be attained for terminals in cells within the femtocell base station during uplink communications to the femtocell base station, and interference applied to the terminals in the macrocell base station can be suppressed. ...


Browse recent Hitachi, Ltd. patents - Tokyo, JP
Inventors: Tomonori YAMAMOTO, Rintaro Katayama, Hirotake Ishii
USPTO Applicaton #: #20120028630 - Class: 4554221 (USPTO) - 02/02/12 - Class 455 
Telecommunications > Radiotelephone System >Zoned Or Cellular Telephone System

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The Patent Description & Claims data below is from USPTO Patent Application 20120028630, Base station and cellular wireless communication system.

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CLAIM OF PRIORITY

The present application claims priority from Japanese patent application JP 2010-170242 filed on Jul. 29, 2010, the content of which is hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a base station and a cellular wireless communication system, and relates in particular to a base station and a cellular wireless communication system that makes uplink transmit power control settings while taking the applied interference into account. The present invention also relates to power control of terminals by base stations in cellular wireless communication system utilizing the orthogonal frequency division multiple access system (OFDMA).

BACKGROUND OF THE INVENTION

A typical configuration for a cellular wireless system is first of all described.

Cellular wireless communication systems are comprised of communication areas called cells which are base stations {sometimes referred to as eNB (e-UTRA Node B)} that cover a particular communication area.

These base stations have different names such as macrocell base stations (MeNB), picocell base stations, and femtocell base stations (HeNB: Home eNB), according to the width, and function of their area. The cellular wireless base station having the largest area is called the macrocell base station which contains terminals (sometimes referred to as UE or User Equipment) within a range from a few hundred to a few thousand meters.

In communication links that couple the base station to the terminal in wireless communication systems, the interference power generated from the neighboring cell base station in the downlink and the interference power from the terminals belonging to the neighboring cell base station in the uplink are known to exert effects on the quality of the communication link. At the cell-edge which is the boundary of the area covered by a base station, the desired signal from that base station\'s own cell must compete with interference power generated from adjacent cells. This interference power causes the SINR (Signal to Interference and Noise Power Ratio) which is an index for expressing received power quality to deteriorate and appears as a drastic drop in communication speed. Lowering the interference from adjacent cells is therefore an essential element in improving the overall system in terms of channel capacity during wireless access.

Transmit power control at the terminal during the uplink operation during wireless access is also closely involved with interference control. This relation is described using FIG. 13. The terminal 13-A in the figure must transmit at high power to overcome the path loss generated between itself and the serving cell base station 11-A (base station to which terminal 13-A belongs) and attain the desired signal (solid line arrows in the figure) at the specified communication quality. However, the high power at which the terminal 13-A transmits arrives at the neighboring cell base station 11-B (broken line arrows in the figure) as interference power which is a large interference power at the terminal 13-B that is connected to the neighboring cell base station 11-B. Conversely, the power from the transmission by the terminal 13-B arrives at the base station 11-A as interference power in the same way and acts as interference power on the terminal 13-A connected to the base station 11-A.

SUMMARY

OF THE INVENTION

The 3rd Generation Partnership Project or 3GPP which is the Standards Development Organization (SDO) is working to establish standards for OFDMA type wireless communication systems called LTE (Long Term Evolution). The transmit power control for the LTE uplink shared (PUSCH: Physical Uplink Shared Channel) is expressed by the following formula as defined in 3GPP TS36.213, “Physical layer: procedures”, v 9.1.0, March 2010.

PPUSCH(i)=min{PMAX,10 log10(MPUSCH(i))+P0—PUSCH+α·PL+ΔTF(i)+f(i)}  [Formula 1]

The base station 11 notifies all the terminals 13 belonging to its own cell of control parameters except for PL (Pathloss). The terminal 13 decides the transmit power utilizing the measured PL and the notified parameter. Each parameter is described later on (See 3GPP TS36.213, “Physical layer: procedures”, v 9.1.0, March 2010 for more detailed information.)

FIG. 14 shows a concept view of the control scheme. The vertical axis is the transmit power. The horizontal axis is the PL between the base station 11 and the terminal 13. The communication quality deteriorates as the PL becomes larger so the terminal 13 must increase the transmit power in order to compensate for the PL. The α or alpha in the formula is a predetermined coefficient for compensating the PL. In this control scheme the PL is fully compensated when the α=1.0, and the received power at the base station (or eNB) is ideally regulated to a specified value. However when the α falls below 1.0 the PL is not fully compensated, and the base station does not maintain the received power at an equal amount among the terminals. When the α equals 0 then the path loss is no longer compensated so transmit power control that is largely dependent on the base power PO—PUSCH is implemented. This scheme is sometimes called the fractional power control equation.

In base stations such as the macrocell base station where deployment over a wide coverage area is essential, the terminal transmit power at the cell-center is set by adjusting the α after determining the transmit power for maintaining communication quality at the cell-edge.

The technology in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-516184 for example discusses a method for setting the uplink target received power quality so as to allow communications within the cell itself, and then raising the uplink target received power quality of the cell-center terminal. This power control method takes the applied interference into account however the terminal itself regulates the transmit power by correcting the target SINR. However this method does not always take into account the extent of interference that adjacent cells apply to each other when this method cannot be applied to all terminals. Here, the base station should preferably provide fixed rules to terminals under its control as broadcast information from the base station.

The femtocell base station installed with the objective of covering hotspots after the macrocell base station was installed, must fulfill the dual tasks of minimizing interference applied to the macrocell base station and achieving high communication throughput with the femtocell base station.

Implementing terminal transmit power control to compensate for the path loss in the femtocell during uplink communication from the terminal to the femtocell base station, achieves high communication throughput at the terminals within the femtocell base station but also increases the applied interference at terminals within the macrocell base station.

In view of the above mentioned problems with the related art, the present invention has the objective of providing a base station for wireless communication systems that controls the transmit power in terminals while both reducing the interference applied to neighboring cells and attaining high communication quality in its own cell during the uplink.

To achieve this objective the present invention controls parameters for uplink transmit power control according to the distribution of terminals within the cell of the femtocell base station.

The femtocell base station collects the terminal distribution within the cell, and selects terminals to represent the cell-center and cell-edge from the terminals within the cell. The femtocell base station further calculates the maximum allowed transmit power of the macrocell for the respective cell-center and the cell-edge terminals within the macrocell. The femtocell base station sets a respective transmit power for the cell-center and the cell-edge that does not exceed the range of the maximum transmit power, adjusts the transmit power control parameters to allow limiting the terminal to the power value that was set, and notifies the terminal.

A first aspect of the present invention to resolve the above problems provides a base station for a cellular wireless communication system comprised of a plurality of base stations and terminals for controlling the transmit power based on specified transmit power control parameters and the path loss with the base station carrying out communication;

in which the base station:

receives from each terminal, the received power quality information of the downlink reference signal from its own base station that was measured by the plural terminals; and the received power quality information of the downlink reference signal from an neighboring cell base station that is adjacent to its own base station;



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stats Patent Info
Application #
US 20120028630 A1
Publish Date
02/02/2012
Document #
13166084
File Date
06/22/2011
USPTO Class
4554221
Other USPTO Classes
455561
International Class
/
Drawings
11



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